We have studied the effect of different fluidizer molecules (especially the Polynaphtalene Sulfonate : PNS and the PolyCarboxylatePolyethoxyle : PCP) on the rheology of gypsum suspensions. The rheology was mainly characterized by the yield stress, the dynamic viscosity and the shear moduli. We have shown, using different size of particles and different lengths for the size of the fluidizer molecules, that the yield stress was inversely proportional to the diameter of the particles and to the square of the distance of separation between the surfaces of the particles. With the help of a model we were able to deduce the thickness of the polymer layer adsorbed on the surface of the particles. The dynamic viscosity of a suspension of crushed gypsum remains large despite the use of fluidizer ; it indicates the presence of aggregates containing several tens of particles. The impurities (divalent ions like Mg2+ or trivalent ions like AI3+ and Fe3+) as well as temperature decrease the efficiency of the PCP either by reducing the interaction between the polymer and the surface of the particles in the case of cations, or by reducing the salvation of polymer in the case of a rise in temperature.
